THOUSANDS of dead fish from coastal fish farms were found in Lim Chu Kang in the past few days, some in the sea and on the shore.

The Agri-Food and Veterinary Authority (AVA) said yesterday that about 90,000kg of fish from farms in the area had died due to the recent hot and dry weather spell.

It said the weather, combined with a lack of rainfall, resulted in low levels of dissolved oxygen in the waters near the farms. Rainfall churns the water, which helps to dissolve atmospheric oxygen in it.

The AVA added that other factors, such as a slight rise in the water's temperature, had also contributed. It has been monitoring the water's condition and had alerted the farms to take precautions such as installing standby aeration systems to add oxygen to the water, said a spokesman.
"As a result, most farms were not affected. The situation has since stabilised and returned to normal. We will continue to work closely with the farms to address any issues they may face," she said, adding that the dead fish came from four farms and included species such as milkfish and mullet.

Singapore has had other instances of mass fish deaths. In December 2009, for example, a plankton bloom killed 400,000 fish in farms off Pasir Ris and Pulau Ubin.

Fish farmers in Lim Chu Kang told The Straits Times that they use water pumps and other machinery to artificially churn the water when there are prolonged periods without rain.

However, this may not help if the natural oxygen levels are too low, said Mr Ong Kim Pit, who has run a fish farm in Lim Chu Kang for 20 years.

Some of the fish can still be sold, but fish farmers are supposed to hire private contractors to dispose of the remainder responsibly, added Mr Ong, who is in his 60s.

On Satuday, a 43-year old man who gave his name only as Andy took his Danish friend to Sungei Buloh Wetland Reserve to show him Singapore's more rustic side.

But instead of mudskippers, monitors and otters, they were faced with the sight and smell of dead fish everywhere.

Andy, a volunteer at the park, said he counted around 150 dead fish that day along the shore of the Sungei Buloh Besar river or stuck in the mangroves.

He said: "The whole area smelled of decomposing matter."

At first he wondered if pollution was affecting the fish in the reserve, but he soon realised that the dead fish were all from two speices: mullet and milkfish, which probably came from the fish farms off Lim Chu Kang.

This was confirmed by a spokesman for the Agri-Food & Veterinary Authority of Singapore (AVA) who said the recent "hot and dry weather with little or no rainfall" had resulted in "low levels of dissolved oxygen in the waters near the coastal fish farms at Lim Chu Kang."

The spokesman said 80 to 90 tonnes of fish, such as milkfish and mullet, from four farms in the area had died, and were in places such as Sungei Buloh.

Mr Malcom Ong, the chief executive officer of Metropolitan Fishery Group, Singapore's largest marine farm which is in the Straits of Johor near Lim Chu Kang, said the oxygen levels had dropped from the early hours of last Thursday to Friday night.

He said that while low oxygen level usually affected only small parts of his farm at a time, allowing this staff to deal with the problem, the low levels of those days were so severe and widespread that he had to prioritise which fish to save.

In the end, his farm lost approximately 40 tonnes (12%) of its milkfish stock, a six-figure loss.

AVA said the farmers affected were advised to dispose of the dead fish by bagging them and placing them in the waste disposal bins.

Additionally, AVA activated a waste disposal company to increase its waste disposal frequencies because of the expected higher amount of waste, the spokesman said.

While Mr Ong said his farm disposed of the dead fish in the bins on mainland Singapore, while trying to rescue its stock, the farm released some dying fish to "at least give them a chance to swim away."

The New Paper understands that the dead fish which had drifted into Sungei Buloh were disposed of by the National Parks staff daily.

Would the dead fish have impacted Sungei Buloh negatively?

Marine ecosystems

Professor Chou Loke Ming from the Department of Biological Sciences, Faculty of Science, National University of Singapore, said marine ecosystems like mangroves would be able to overcome an overload of dead fish over time.

He added: "Normal ecological processes will break down the carcasses" and return the remains back to the food chain, noting that the only significant impact of around 100 tonnes of dead fish spread over a large area would be the stench.

Ms Ria Tan, a nature blogger and environmentalist, can attest to this fact. Yesterday, she went to survey the mangroves at the end of Lim Chu Kang Road to see the situation for herself.

Blogging about her experience, she said she could smell the fish long before she could see them.

AVA said the water conditions have stabilised and are now back to normal. It has conducted a workshop for farmers on possible measures to deal with such situations, and will continue working closely with the farms to take care of any future issues.

Mass fish death causes

Professor Chou Loke Ming from the Department of Biological Sciences, Faculty of Science, National University of Singapore, said fish deaths can also be caused by

1. Sudden and large discharges of toxic pollutants.

2. Overstacking fish in cages in sheltered waters with little water flow, leading to a lack of dissolved oxygen.

3. Algal blooms which also lower the dissolved oxygen in the water.

In the past few years, Singapore has been a few cases of mass fish deaths.

29 March 2012: More than 1,000 dead saltwater fish called baby tamban washed up along Sungei Tampines.

Tonnes of fish from four farms at the Lim Chu Kang area have died due to the lack of oxygen in the water, said the Agri-Food & Veterinary Authority (AVA).

Some of the close to 90,000kg of dead fish, mainly mullet and milkfish, have also been sighted at Sungei Buloh Wetland Reserve (SBWR).

According to a statement by the AVA, the lack of oxygen is due to the recent hot and dry weather conditions with little rainfall.

Rainfall is important to produce a “churning effect”, which helps to dissolve “atmospheric oxygen” in the water, it said.

Other factors such as “slightly warmer temperatures” have also contributed to the mass death.

Spotted by bloggers

The mass death was initially brought to light on 29 June after a blogger posted photos of the dead fish found on Lim Chu Kang beach as well as at SWBR. The nature lover, who was on a walk with a friend, snapped photos of fish stuck on rocky bunds and trees at SBWR's mangrove boardwalk area.

According to his entry, some of the fish found at SBWR were already producing a “pungent smell of decomposing fish”. He added that he the “SWBR staff had cleared what they could reach but there were just too many”.

On Monday, Ria Tan from nature site “Wild Shores of Singapore” followed up with more photos of the dead fish at Lim Chu Kang.

“The dead fish looked like those raised by fish farms,” she wrote.

Proper disposal

The AVA has advised affected farmers to dispose the dead fish and has increased “the frequency of waste disposal” by activating waste disposal companies. It is also working closely with the farms to help with the situation and provide assistance.

One way for farmers to “mitigate” the low levels of oxygen in the water, is by setting up “standby aeration systems”, according to the AVA and it is rendering the necessary assistance.

SINGAPORE: Thousands of dead fish have been found floating at sea and on the shore at the Lim Chu Kang area as well as the Sungei Buloh Wetland Reserve.

The dead fish were among 90 tonnes of fish belonging to four farms in the Lim Chu Kang area.

AVA said the fish have died due to lack of oxygen in the water. This, it said, was caused by the hot and dry weather which lowered the level of dissolved oxygen in the water.

AVA has been working closely with local farmers to encourage good farm practices which include properly bagging dead fish and disposing of them in bins.

Fish farms in Singapore are licensed by AVA. Under the conditions of licensing, coastal fish farms have to ensure that waste generated from their operations are properly disposed of in approved waste containers on land.

However, AVA noted that during the farms' emergency operations to remove the dead fishes for disposal, some could have dropped into the sea and got washed ashore.

In anticipation of more waste, AVA said it had activated the waste disposal company to increase the frequency of disposal.

Three additional trips were made on top of the usual trip to clear waste last weekend.

“We will take enforcement action if farms are found to be disposing their farm waste into the waters. In addition, we work with relevant agencies to detect illegal dumping of waste into the sea by fish farms," said a spokesman from AVA.

Under the Fisheries Act, any person who illegally disposes of dead fish into the waters can be jailed up to 12 months, and fined up to S$10,000.

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